The present invention relates to an apparatus that allows for the exchange of gases in a liquid sample. More specifically, the invention relates to a blood oxygenator, which allows external oxygen to be incorporated into a blood sample while carbon dioxide is removed from the sample.
The invention includes several features that make it particularly well suited for use as an artificial lung. Indeed, the apparatus according to the present invention has several characteristics that make it suitable for use in an extracorporeal bypass circuit, as well as a temporary in vivo replacement for a mammalian lung.
Blood oxygenators are frequently used to accomplish the gas exchange functions normally performed by the lungs. Conventional blood oxygenators contain a gas exchange medium positioned adjacent a flowing stream of blood. When attached to an oxygen supply, the blood is perfused with oxygen and carbon dioxide is removed.
Typically, these devices are utilized when a patient""s lungs are temporarily disabled. The situations in which a patient needs a blood oxygenator can generally be classified into two types: short term and indefinite term. Open heart surgery provides an example of a short-term need for a blood oxygenator. During this procedure, a patient""s heart can be stopped temporarily. To continue vital functions of the circulatory system, an extracorporeal bypass circuit is constructed, in which a pump sends the patient""s blood through a series of devices. A blood oxygenator is frequently included in these circuits so that the patient""s blood can continue to deliver oxygen to the tissues of the body.
The prior art provides several examples of blood oxygenators that are suitable for use in these extracorporeal bypass circuits. Unfortunately, the use of these external circuits are not ideal for situations in which the need for an artificial blood oxygenator spans an indefinite term. The extracorporeal bypass circuits are bulky, labor intensive, and expensive to operate. For these reasons and more, these circuits are typically only used to manage the blood oxygenation needs of the indefinite term patient who requires long term intensive care.
Many indefinite term patients are those awaiting a lung transplantation procedure, which has become a well-established clinical procedure for several respiratory maladies, including chronic obstructive pulmonary disease, emphysema, cystic fibrosis, and idiopathic pulmonary fibrosis. Unfortunately, many patients who would benefit from a lung transplant must wait to receive a suitable lung. Furthermore, immunosuppressive therapy, which is commonly used prior to transplantation procedures, is generally a contraindication to extracorporeal support, such as by a bypass circuit, due to the risk of bacterial infections.
As a consequence, there is a need for a blood oxygenator that is suitable for use in indefinite term patients. A blood oxygenator that is able to provide gas exchange functions without imposing a significant load onto the heart would be particularly desirable. Furthermore, an implantable blood oxygenator, which could effectively serve as an artificial lung, would enhance the lifestyle of indefinite term patients and provide a bridge therapy to lung transplantation.
The present invention provides an apparatus that allows for exchange of gases in a liquid sample. In a particularly preferred embodiment, the invention provides a blood oxygenator. The blood oxygenator according to the present invention has several characteristics that make it suitable for use as an artificial lung in indefinite term patients.
In one embodiment, the apparatus according to the present invention comprises a housing having an inner surface, a first end and a second end. The housing defines an interior chamber that has inner and outer portions. A gas exchange medium is disposed in the outer portion of the interior chamber, and a separator is disposed in the inner portion. The separator preferably extends substantially along the length of the gas exchange medium.
The apparatus includes first and second inlets and first and second outlets.
The first inlet is adapted to introduce a stream of liquid into the interior chamber, on an axial path extending from the first end of the housing to the second end, and preferably directed toward the separator.
The first outlet allows the liquid to exit the apparatus after flowing through or past the gas exchange medium. In the application described in detail herein, the first inlet and outlet serve as a blood inlet and outlet.
The second inlet and second outlet are adapted to introduce and carry away, respectively, gas from the gas exchange medium. In the application described herein, the second inlet and outlet serve as an air or oxygen inlet and outlet.
The separator functions to radially divert the stream of liquid off its axial path and toward the gas exchange medium. Consequently, the liquid flows principally radially through the gas exchange medium.
The outer portion of the housing""s chamber may further define a circumferential collection gap that collects liquid exiting from the gas exchange medium and directs it toward the first outlet.
Preferably, the housing and first outlet both have a generally elliptical cross-sectional shape. Particularly preferable, the ovoid shapes of these elements are oriented such that a major axis of the elliptical shape of one element is substantially perpendicular to a major axis of the elliptical shape of the other element.
The apparatus of the present invention may also include a compliant chamber placed on a communicative passageway that carries liquid to the first inlet. In a preferred embodiment, the complaint chamber comprises a relatively non-elastic chamber formed by the communicative passageway. One end of the chamber can be fixedly attached to a surface while another end remains adjustable. Alternatively, the compliant chamber can be formed of an elastic material. Also alternatively, the compliant chamber can be placed in a sealed container having a fluid that surrounds the chamber. Furthermore, one or more springs could be utilized to store energy and provide the desired compliance.
The apparatus may further comprise a means for warming and/or cooling the liquid being passed through the device. In one embodiment, a conductive element, such as electrical tape, is disposed on the separator. The electrical tape is responsive to an external temperature regulator and warms the liquid, such as blood, when an electrical current passes through the tape.
The present invention provides an apparatus with impedance characteristics that allow it to be incorporated into the circulation without placing a significant load on the right heart. Indeed, the impedance characteristics of the blood oxygenator according to the present invention allows for perfusion of the oxygenator by the native circulation without detrimental effects on the right ventricle.